Page 23 - Q & A STPM 2022 Physics

Physics Semester 2 STPM Chapter 14 Electric Current

14.2 Drift Velocity

Section A Multiple-choice Questions

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Question 1
A conductor of cross-sectional area 0.10 mm carries a current of 2.5 A. If the
2
number of conduction electrons per cubic metre is 1.0 × 10 m . What is the
–3
28
value of drift velocity of the free electrons in the conductor?
–2
A 1.6 × 10 m s C 3.0 × 10 m s –1
–3
–1
B 3.9 × 10 m s –1 D 6.2 × 10 m s –1
–3
–2
Answer: A
I = nAve
v = I
nAe
= 2.5
(1 × 10 )(0.1 × 10 )(1.6 × 10 )
28
–6
–19
= 1.56 × 10 m s –1
–2
Question 2
Which statement is true about the drift velocity of the electrons in a current-
carrying metallic conductor?
Semester
A It is directly proportional to the diameter of the conductor.
2 B It is inversely proportional to the current.
C It is inversely proportional to the number of conduction electrons per unit
volume.
D It is directly proportional to the resistance of the conductor if the potential
difference across the conductor is kept constant.

Answer: C
v = I ,
Exam Tips
nAe Exam Tips
1
v ∝ I , v ∝ R Formulae used
v ∝ 1 • I = nAve
n • I = V
v ∝ 1 ∝ 1 R
A d 2

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014 STPM Q&A Physics T2.indd 222 17/02/2022 10:12 AM